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2008 Qeshm earthquake
The 2008 Qeshm earthquake occurred at 14:30 IRST (11:00 UTC) on 10 September. It had an epicenter on the island of Qeshm, close to the location of the 2005 Qeshm earthquake. It had a magnitude of 5.9 on the moment magnitude scale and caused seven deaths and 30 injuries. It was followed by five aftershocks of M 5.0 or greater over the next ten months.〔
==Geological setting==
Iran lies within the complex zone of collision between the Arabian Plate and the Eurasian Plate;〔 near Qeshm the rate of convergence is about 25 millimeters annually.〔Nissen et al. 2007, pg 2.〕 Part of this convergence is accommodated by shortening within the Zagros fold and thrust belt, with the remainder occurring to the north of the Iranian Plateau. The most active part of the Zagros is the 'Simply Folded Belt', which is characterised by large folds formed above a layer of Neoproterozoic Hormuz salt, which locally reaches the surface in the crests of some anticlines as salt diapirs.〔 The sedimentary rocks above the salt layer comprise a basal Cambrian conglomerate and a thick sequence of limestones of Palaeozoic to Upper Cretaceous age, known together as the 'Competent Group' due to their relatively high competence, followed by a sequence of mechanically weaker marls and interbedded limestones of latest Cretaceous to Lower Miocene age topped by Neogene sandstones and conglomerates. There is evidence of intermediate level detachment at some of the weaker layers, leading to folds at different stratigraphic levels have different locations, orientations or wavelengths.〔Nissen et al. 2010, p. 183.〕 Earthquake focal mechanisms and hypocentral depths show that shortening is accommodated by a mixture of high-angle and low-angle reverse faulting, within either the lowest part of the sedimentary cover or in the basement beneath the Hormuz salt.〔Talebian et al., pp. 506–526.〕
The island of Qeshm is elongated WSW–ENE, parallel to the coastline and the regional trend of the main fold axes. It is formed of Neogene sediments apart from a diapir of Hormuz salt that pierces through to the surface at the western end of the island. The sediments are affected by a series of large, mainly anticlinal folds that show a variety of trends in the central part of the island. The axis of the Laft anticline runs mainly NW–SE, while the Salakh anticline trends roughly W–E and the Suza anticline and Ramkan syncline trend SW–NE. The island shows clear evidence of recent uplift in the form of marine terraces, with the highest terrace identified at above sea level. An uplift rate of 0.2 millimeters annually has been estimated from Uranium series dating of aragonite from corals on the terraces.〔Nissen et al. 2007, pp. 2–3.〕
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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